1. Field of the Invention
The present invention relates to a sustained release preparation. More specifically, it relates to a sustained release preparation in which a combination of (a) a non-anionic cellulose ether and (b) a methoxyethylene-maleic anhydride copolymer or the hydrolyzate thereof is utilized as a sustained-release agent.
2. Description of the Related Art
Techniques for the sustained release of preparations have long been studied, to control the dissolution or release and absorption of medicaments from the preparation in human organs upon administration. For example, it is known in the art that medicaments coated by various film-forming substances or medicaments are included or encapsulated in matrices composed of waxes or polymers. However, generally speaking, these known techniques are disadvantageous in that the production processes are complex and the desired sustained release cannot be satisfactorily attained.
In view of the state of the art as described above, the present inventors investigated the conditions for releasing with certainty medicaments in living bodies, and consequently found that two conditions are necessary for this purpose: (1) that the preparation should have an affinity for the tissue or the organ at the site where the preparation is administered, and (2) that the preparation should easily retain its form without being rapidly dissolved or digested with body fluids (form retentivity). Accordingly, the inventors investigated preparations which are endowed with these two conditions and can be easily prepared.
As the compounds which have heretofore been employed in the cosmetics or pharmaceuticals industries, there are methoxyethylen-maleic anhydride copolymers, which have an excellent affinity with components of living bodies such as mucosa of digestive organs, muscles, and fat tissues, and a large number of application examples of these compounds for pharmaceuticals can be found. It has been reported that the dissolution or release of ephedrine from tablets containing a methoxyethylene-maleic anhydride is delayed (E. Chalhoub et al, Pharm, Ind., 1976, 38 (9), 844-7). Since, however, a methoxyethylene-maleic anhydride is readily soluble in water, when tablets containing a methoxyethylene-maleic anhydride are actually administered to living bodies, the tablets are quickly dissolved, and thus the release of the medicaments cannot be sustained.
Certain kinds of cellulose derivatives, for example, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, ethyl cellulose, chitin, and chitosan, all have a high form retentivity through gellation with moisture, and are expected to delay dissolution or release of the coexisting medicaments. U.S. Pat. No. 4,126,672 discloses a process for the production of a sustained release preparation employing hydroxypropylmethyl cellulose. Nevertheless, although these gel forming polymers have a high form retentivity and are preferable for the sustained release of the co-existing medicaments, since they form gels which cannot be rapidly dissolved or digested with body fluids, they lack adhesiveness to or affinity with living bodies. For example, when these gel forming polymers are filled together with medicaments in hard capsules and orally administered into living bodies, they will be rapidly moved into the digestive organs, and thus insufficient absorption will frequently occur.
To the inventors' knowledge, no example of the use of a mixture of a methoxyethylene-maleic anhydride copolymer with a cellulose derivative for a sustained release preparation has yet been reported. U.S. Pat. No. 4,172,055 discloses a mixture of hydroxypropylcellose with poly (maleic anhydride/alkene-1) as a useful gelling agent, and methoxyethylene-maleic anhydride/alkene-1). The above U.S. patent, however, provides a fluid for hydraulics as an aqueous solution of the above mixture to be used for a drill for use in the excavation of mineral sources such as petroleum, and an investigation has not been made concerning the application thereof for sustained-release preparations.